In the construction of horizontal blinds, particularly in wood blinds, two kinds of controls are desired. The blind should have a control to lift the slats of the blind. In addition, the blind should permit control over the tilt of the slats. Traditionally, two separate operating mechanisms were used to provide the desired control. One device would exclusively control the lifting of the blind while another independent device would control the tilt position of the slats. A single mechanism controlling both functions is preferred.
There are a limited number of prior art mono-controlled lifting and tilting mechanisms. One such system is disclosed in Rude et al. U.S. Pat. No. 5, 228,491. In this device, the tilting function is controlled by the position of flexible plastic arms that may be adjusted by rotation of a shaft on which the tilters are centered. A frictional relationship between the tilter and the shaft allows the flexible tilter to rotate with the shaft rotation in either direction until stopped at limit positions. However, the complex structure of the tilter, which itself provides the varying frictional force on the shaft as a function of the weight of the slats of the blind, limits the application of the device. The structure is difficult to manufacture and may not be appropriate for heavier blinds because the weight makes tilting more difficult. Moreover, when winding the lifting cord, unnecessary transverse movement in addition to rotation is utilized to manage the coils of the lifting cord.
Another such system is disclosed by Marocco, U.S. Pat. No. 5,628,356. This system makes use of tape as the lifting medium. A winding reel collects the tape when the blind is lifted. However, the system does not provide a workable solution for managing a lifting cord. Moreover, tape lift systems are not practical for lifting some blinds such as large wood blinds. Inner holes in the wood have inherently very sharp edges that cause cutting of the tape and will lead to lift failure.
One other known mechanism relies on the constant rotation of the shaft to achieve a tilt. In this invention, the two sides of the ladder cord are joined together in a loop and placed in a V-groove of the tilting mechanism. Constant rotation of the mechanism drags the cord along and creates a tilt. At the same time the lift cord, which is attached to the rotating shaft portion of that mechanism, gathers on the shaft. However, tilting horizontal slats with a V-groove device was never a preferred way of achieving a tilt. The positioning of the slats cannot be accurately controlled. Sometimes, especially on lightweight blinds, the device is not reliable because almost the entire weight of the blind in being supported by the lift cord. This leaves the ladder cord with out much tension in the V-groove and can lead to tilt failure.